97 F-250 small problem

My 97 250 with the 351 sometimes when shifting from 1st to 2nd (Automatic trans)makes a loud wierd exhaust noise. it doesnt lose power, just a strange noise. Only happened 3 times in the last 2 months. Anyone had this happen to them or know about this??
Thanks
SJR

Is this the regular F250 that is the new style or the Heavy Duty old style 97 F250. I have the HD old style 97 with the 351, automatic transmission and I've never experianced this problem. How many miles do you have on it?

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^One of the lawns we mow

It is under warranty, but its such a slight problem, it would hardly be worth losing a day to take it to my Ford dealer to check it out. I was just wondering if anyone else has experienced this with theirs. the noise is very hard to explain, its like a whirl sound when it shifted from 1st to second gear & it only happened a couple of times.
SJR